The subject invention relates to a pump assembly having a controlled mixing ratio for metering plural fluids.
Pump assemblies are presently available for metering, and subsequently mixing, prescribed volumes of fluids. These assemblies generally comprise independently driven pumps, where each pump supplies a separate fluid to a common discharge line where the two fluids are mixed. The two fluids are mixed in proportion to the volumetric flow rates of the pumps to provide the required mixture ratio flow rate of the mixed fluid. For example, if the required flow rate of the mixed fluid is 6 gallons per minute (GPM), and the prescribed mixing ratio is 5 to 1, two pumps are chosen which provide 5 GPM and 1 GPM, respectively.
In practice, the design of such an assembly is not so simplistic as the above example, as most applications also require the pump assembly to provide a variable range of available mixed fluid flow rates, while still maintaining a constant mixing ratio. In order to vary the flow rate of the mixed fluid, the speed of the individual pumps must be variable, to provide a range of output flow rates for the individual fluids.
Therefore, the two pumps are typically driven independently by electric motors, where one of the motors has a device for sensing the rotational speed of the motor drive and providing a feedback signal to the other drive motor, to vary the speed of the other pumps accordingly. The flow rate of the mixed fluid is controlled by varying the pump with the sensor, and the other is varied, vis-a-vis the feedback, to maintain the given mixing ratio.
One of the disadvantages to the above-mentioned device is that there is a response time involved in varying the second motor speed, and during such time, the mixing ratio is fluctuating. Furthermore, the device is not useable in applications where the required flow rate of the mixed fluid is constantly varying, as the response time involved is too high to ever produce a steady state fixed mixing ratio.
This pump assembly is also cost prohibitive for many applications, due to the design complexity. As mentioned above, the assembly includes two separate pumps and motors, feedback equipment for sensing the speed of the main motor, and means to receive the feedback signal to calibrate and adjust the speed of the follower motor in order to maintain a constant flow rate.
An object of the invention then is to provide an apparatus for maintaining a fixed mixing ratio of two fluids irrespective of the required mixed fluid delivery flow rate.
A further object of the invention is to provide a metering apparatus which is not cost restrictive and is available for numerous applications.
Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.